Sleep and Memory
All of us are only too familiar with the importance of sleep and are aware of what happens when we are sleep deprived. Sleep helps to rest the body and brain and serves to refresh our mind. Since the brain is mainly responsible for inducing the sleep state, an obvious, close association exists between sleep and the brain. In this context, it is interesting to examine the relationship between sleep (or rather the lack of it) and memory functions.
Many sleep researchers and clinicians have asked the question of “How sleep affects our memory”. In order to address this question, numerous scientific studies have been carried out, both on animals as well as on human beings. Results from almost all such studies clearly show that sleep deprivation, both short term and long term, negatively influences memory functions. Specifically, lack of sleep affects certain stages and certain types of memory functions.
A series of animal studies and human experiments have revealed that the type of memory that is most significantly affected by sleep deprivation is cognitive or skill memory. Skill memory refers to our ability to remember a newly learned skill such as a sequence of limb or finger movements. Sleep deprived subjects of the study performed markedly poor on a variety of tasks that tested skill memory functions.
Other experiments have looked at the actual stage of memory formation that is affected by sleep deprivation. Such experiments strongly point out that sleep is important in memory consolidation. Memory consolidation is the stage in which newly acquired short term memories are “replayed” in the neuronal circuits of the brain, eventually resulting in the formation of long-term memories.
Importantly, research into the relationship between sleep and memory has also shown that it is the REM (Rapid Eye Movement) sleep that is involved in memory consolidation. During REM sleep, both the brain as well as the body attains a state that is similar to the wakefulness state. Dreaming is a brain activity that is believed to occur during this period and may reflect the fact that memories are being replayed in the brain through repeated firing of neuronal circuits to further strengthen the neuronal connections.
The REM sleep phase is also believed to catalyze memory consolidation by causing reverse learning. In reverse learning, huge amounts of information (that is deemed unwanted by the brain) acquired by the senses during the daytime are eliminated in order to prevent information overload in the brain. The brain structure called hippocampus is important for many of these processes.
There is also some evidence to show that lack of sleep also adversely affects recall memory or memory relating to logical tasks. Human volunteers, who were sleep deprived for more than thirty-five hours, gave poor performances in recollecting the information that they had learned from textual material immediately prior to undergoing sleep deprivation.
There is an important last point to consider. Although, sleep deprivation of a few hours for a couple of nights may not cause noticeable memory impairment (because our body has other mechanisms to compensate for it), chronic sleep deprivation has been shown to cause significant memory impairment. Scientists have compared the memory loss of a chronically sleep deprived person to the memory impairment that results from aging! Yet another good reason to get a good night’s sleep!